In a number of design applications, particularly in the automotive industry, it is essential to provide structural members which are light-weight and yet which have high strength characteristics. A number of exotic metal alloys and the like have been proposed by others in the past for use in forming high strength structural members; however, in some applications, including in the automotive industry, the cost of these alloys is typically prohibitive. Accordingly, there is a need for structural reinforcement members which are light-weight and low-cost and which can be used to compliment existing design structures.
There is a considerable body of prior art dealing with the reinforcement of motor vehicle structural components. In U.S. Pat. No. 4,901,500, entitled “Light-Weight Composite Beam,” a reinforcing beam for a vehicle door is disclosed which comprises an open channel-shaped metal member having a longitudinal cavity which is filled with a thermosetting or thermoplastic resin-based material. In U.S. Pat. No. 4,908,930 entitled, “Method of Making a Torsion Bar,” a hollow torsion bar reinforced with a mixture of resin with filler is described. The tube is cut to length and charged with a resin-based material.
In U.S. Pat. No. 4,751,249, entitled “Reinforcement Insert for a Structural Member and Method of Making and Using the Same,” a precast reinforcement insert for structural members is provided which is formed of a plurality of pellets containing a thermosetting resin and a blowing agent. The precast is expanded and cured in place in the structural member. Also, in U.S. Pat. No. 4,978,562, entitled, “Composite Tubular Door Beam Reinforced with a Syntactic Foam Core Localized in the Midspan of the Tube,” a composite door beam is described which has a resin-based core that occupies not more than one third of the bore of a metal tube.
In co-pending U.S. patent application Ser. No. 245,798 filed May 19, 1994, entitled “Composite Laminate Beam for Automotive Body Construction,” a hollow laminate beam characterized by high stiffness-to-mass ratio and having an outer portion which is separated from an inner tube by a thin layer of structural foam is described.
Although in some applications, there are advantages to these prior art reinforcement techniques, there is a need to provide a reinforcement for rail sections which significantly increases the strength of the rail, particularly at stress points, in a manner which is not only low-cost, but also which adapts readily to mass production assembly.
In addition, it is known that cyanoguanidine is a commonly-used latent curing agent for foamed epoxy polymers. The most frequently used material has a nominal particle size of about 80 microns. For higher reactivity, micronized versions are sometimes used, e.g. 90% of particles less than 30 microns. In the prior art, conventional usage of curing agents may cause “burning” of the foamed polymer. This is because the heat from the exothermal curing reaction does not readily dissipate. This solution is, however, not practical when the temperature of the oven is pre-set for other conditions, i.e., paint curing the like.